Soon after computers first became widespread, attempts were made to communicate with the computer by means of a display device. Initial efforts generally involved the use of a keyboard terminal and a cathode-ray tube (CRT) capable of depicting alpha-numeric characters based on input of the keyboard or output from the computer. Soon thereafter, the cathode-ray tube became an interactive unit itself wherein the computer operator could select, by means of a ligh-sensitive probe or a touch-sensitive surface, various options displayed by the cathode-ray tube. Almost concurrently, the engineering profession developed design programs wherein machinery design and the like could be accomplished by means of a light pen passing over the face of a cathode-ray tube so that the path followed by the light pen became the design for the machinery.
When using CRT's for selectively choosing a particular alternative presented on the surface of the visual display device, the selection processes may be in the form of a menu, that is, a lising of alternatives, or a tree structure. The menu or tree structure may be continued through three or four different displays in more complex problems. Alternatively, a diagram may be displayed on the CRT which prompts responses from the user. The purpose of these interactive terminals using either a light pen or a touch-sensitive device is to avoid the use of a keyboard-type terminal. Further, such devices take advantage of man's instinct to select by pointing. Present-day touch-sensitive devices pick up the coordinates of the selected point on the touch sensitive surface and transmit the coordinates to the machine for further manipulation. One drawback with the present machines utilizing the touch-sensitive input is the sensitivity of the surface material, thus necessitating a good deal of care on the part of the operator. This, of course, inhibits widespread use of such terminals due to the inherent problem of damage that may occur to the surface. A further inhibition to widespread use of a touch-sensitive terminal has been the inordinate cost in comparison with keyboard devices. Thus, high cost prohibits widespread usage, while sensitivity requires a good deal of training to learn to use the device to its fullest advantage without damaging the device. An example can be found in a design situation where each engineer may have one or two drawing boards which are available to him on a full-time basis, while the entire engineering design facility may have only one or two terminals to be utilized by the engineers in the more complex design situations.
In addition to the above drawbacks, the touch-sensitive surfaces have degraded the image on the display device by reducing light transmission to an unacceptable level, creating a glare on the surface, or degrading contrast. Furthermore, existing touch-sensitive devices have generally required a rectangular sheet of relatively rigid uniformly conductive material in order to use Cartesian coordinates. Since most video display devices are non-rectangular, the useful screen area may be reduced by an amount necessary to accommodate the touch-sensitive device. Finally, the typical display device does not exhibit a non-deformed image; thus the coordinate obtained on the screen does not necessarily correspond to the actual coordinates of a traced image.
In a more mundane environment where a menu is selected, it is envisioned that cheap interactive terminals could be used in the airline reservation business. For example, each ticket agent and each check-in clerk associated with a particular flight would be provided with a graphic display device on which a diagram of the plane and all its seats would be displayed. The agent or check-in clerk could then select the appropriate seat for the passenger without the necessity of "keyboarding" of the seat number and other information that might be required of the various reservation systems. Such a system has not been available in the past by the high cost of interactive video display terminals, not to mention the training required to use such terminals.